JP5573632B2 - Group III nitride semiconductor light emitting device - Google Patents

Description

  The present invention is to improve light extraction efficiency without deteriorating crystallinity in a method for manufacturing a group III nitride semiconductor light-emitting device having a surface other than the c-plane as a main surface.

  A method for obtaining a GaN crystal having a nonpolar surface such as an m-plane or a-plane or a semipolar plane such as a (11-22) plane by subjecting the sapphire substrate to irregularities and growing GaN crystals from the irregular sides. Is known (Patent Document 1). Such a group III nitride semiconductor light emitting device having a nonpolar surface or semipolar surface as a main surface has a small internal electric field, so the recombination rate between electrons and holes can be increased, and the internal quantum efficiency can be expected to be improved. Currently, development is actively underway. The concavo-convex shape provided on the sapphire substrate is preferably a stripe shape rather than a dot shape in which concave portions or convex portions are periodically arranged. This is for reducing the variation in the plane orientation of the GaN crystal and improving the crystallinity.

JP2009-203151A

  However, when the uneven shape provided on the sapphire substrate is a stripe shape, there is no unevenness in the direction along the stripe direction. Can not be taken out.

  If the concavo-convex shape provided on the sapphire substrate is a dot shape in which dot-shaped concave portions or convex portions are arranged periodically, the light extraction efficiency can be improved as compared with the case of the stripe shape. The variation in the plane orientation of the film becomes large, and the crystallinity is deteriorated.

  Accordingly, an object of the present invention is to provide a group III nitride semiconductor light-emitting device in which a laminated structure composed of a group III nitride semiconductor having a nonpolar surface or a semipolar surface as a main surface is formed on a striped uneven substrate. In the manufacturing method, the light extraction efficiency is improved without deteriorating the crystallinity of the group III nitride semiconductor.

  In the first invention, a stripe shape is formed on the surface of the sapphire substrate, and a group III nitride semiconductor is crystal-grown from the concavo-convex side surface due to the stripe shape, whereby a nonpolar plane or a semipolar plane is the main surface on the sapphire substrate. In a method for manufacturing a group III nitride semiconductor light-emitting device that forms a stacked structure of group III nitride semiconductors, stripes are formed on the surface of a sapphire substrate in parallel with a first direction that is parallel to the main surface of the sapphire substrate. A first step of forming a stripe shape constituted by a plurality of arranged first grooves; a second step of forming an insulating film on the entire surface along the first stripe shape on the surface of the sapphire substrate; And a third step of forming a resist mask in a stripe shape in which the second direction that forms an angle with the first direction is a stripe direction, and is not covered with the resist mask. The insulating film in the region is dry-etched, and then the sapphire substrate exposed thereby is dry-etched until the bottom surface of the etching becomes flat, thereby forming a second stripe shape and removing the resist mask. Then, from the exposed surface perpendicular to the main surface of the sapphire substrate exposed in the fourth step, a group III nitride semiconductor is crystal-grown in a direction perpendicular to the exposed surface by MOCVD, and the main surface is formed as a nonpolar surface or a semipolar surface. And a fifth step of forming a semiconductor layer made of a group III nitride semiconductor. A method for manufacturing a group III nitride semiconductor light-emitting device.

Here, the group III nitride semiconductor is a semiconductor represented by the general formula Al _x Ga _y In _z N (x + y + z = 1, 0 ≦ x, y, z ≦ 1), and a part of Al, Ga, and In Are substituted with other group 13 elements B and Tl, and part of N is substituted with other group 15 elements P, As, Sb, Bi. More generally, GaN, InGaN, AlGaN, or AlGaInN containing at least Ga is shown. Usually, Si is used as an n-type impurity and Mg is used as a p-type impurity.

  The nonpolar plane or the semipolar plane is a plane having an internal electric field of 10% or less with respect to the internal electric field in the case of the c plane. For example, non-polar surfaces such as m-plane, a-plane and (11-24) plane forming 90 ° with respect to c-plane, (11-22) plane forming about 60 ° with respect to c-plane, (20- 21) planes, (10-11) planes, (10-12) planes and other semipolar planes.

In the fourth step, until the bottom surface of the etching becomes flat does not mean that the etching is completely flat, but in the subsequent fifth step, crystal growth from the exposed surface perpendicular to the main surface of the sapphire substrate dominates. It may be flat as long as desired. Note that when the convex portion of the sapphire substrate is dry-etched, the corner of the convex portion is rounded as the etching progresses, and the height of the convex portion is gradually lowered. The fourth step uses this to flatten the bottom surface of the etching.

As a material for the insulating film, SiO ₂ , Si ₃ N ₄ , ZnO, TiO ₂ , ZrO ₂ , or the like can be used. The thickness of the insulating film is desirably 5 to 100 mm because of the ease of dry etching of the insulating film in the fourth step.

  The angle formed between the first direction and the second direction is preferably 30 to 150 °, and most preferably 90 °, in order to improve light extraction efficiency. Similarly, in order to improve the light extraction efficiency, it is desirable that the angle formed by the first groove side surface with respect to the main surface of the sapphire substrate is 40 to 80 °.

  A second invention is a method for producing a group III nitride semiconductor light emitting device according to the first invention, wherein the first direction and the second direction are perpendicular to each other.

  In a third aspect based on the first aspect to the second aspect, the nonpolar plane is the m plane, the a plane, the (11-24) plane, the semipolar plane is the (11-22) plane, (20- 21) a group, a (10-11) plane, and a (10-12) plane.

A fourth invention is a group III nitride according to the first to third inventions, wherein the sapphire substrate has an a-plane as a main surface, and the first direction is the c-axis direction of the sapphire substrate. It is a manufacturing method of a semiconductor light emitting element.
According to a fifth aspect of the present invention, in the first to third aspects, the exposed surface perpendicular to the main surface of the sapphire substrate exposed by the fourth step is a c-plane of sapphire. The semiconductor is characterized by crystal growth in the c-axis direction of the group III nitride semiconductor parallel to the main surface of the sapphire substrate.

  According to the method for manufacturing a group III nitride semiconductor light emitting device of the present invention, it is possible to improve the light extraction efficiency without deteriorating the crystallinity of the group III nitride semiconductor mainly having a nonpolar plane or a semipolar plane. Can do.

FIG. 3 is a diagram showing a configuration of a group III nitride semiconductor light-emitting device of Example 1. The figure which showed the uneven | corrugated shape of the sapphire substrate 10 surface. The figure which showed the formation process of the uneven | corrugated shape to the sapphire substrate 10 surface. FIG. 3 is a view showing a manufacturing process of the group III nitride semiconductor light emitting device of Example 1.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram showing a configuration of a group III nitride semiconductor light emitting device of Example 1. The group III nitride semiconductor light-emitting device of Example 1 includes a sapphire substrate 10 having a surface with a concavo-convex shape as a main surface, and a concavo-convex shape side surface of the sapphire substrate 10 via a buffer layer (not shown). The base layer 18, the n-type layer 11, the light emitting layer 12, and the p-type layer 13, which are made of a group III nitride semiconductor having an m-plane as a main surface, are sequentially stacked. These n-type layer 11, light emitting layer 12, and p-type layer 13 correspond to the laminated structure in the present invention. Partial regions of the light emitting layer 12 and the p-type layer 13 are removed, and the n-type layer 11 is exposed. An n electrode 14 is formed on the exposed n-type layer 11. A transparent electrode 15 made of ITO is formed on almost the entire surface of the p-type layer 13, and a p-electrode 16 is formed on the transparent electrode 15. The group III nitride semiconductor light emitting device of Example 1 is a face-up type device.

  The n-type layer 11, the light emitting layer 12, and the p-type layer 13 may have any conventionally known structure. For example, the n-type layer 11 has a structure in which an n-type contact layer made of GaN and doped with Si at a high concentration and an n-clad layer made of GaN are sequentially laminated from the sapphire substrate 10 side. For example, the light emitting layer 12 has an MQW structure in which a barrier layer made of GaN and a well layer made of InGaN are repeatedly stacked. For example, the p-type layer 13 has a structure in which a p-cladding layer doped with Mg made of AlGaN and a p-contact layer doped with Mg made of GaN are stacked in order from the light emitting layer 12 side.

  FIG. 2A is a perspective view showing the concavo-convex shape applied to the surface of the sapphire substrate 10, and FIG. As shown in FIG. 2, the uneven shape is a shape in which a first stripe shape 100 is formed on the surface of the sapphire substrate 10 and a second stripe shape 101 is formed so as to be orthogonal to the first stripe shape 100. is there.

  In the first stripe shape 100, a plurality of first grooves 100a are arranged at equal intervals in parallel to a predetermined direction (the x-axis direction in FIG. 2, which corresponds to the first direction of the present invention). The x-axis direction is the c-axis direction of the sapphire substrate 10. The m surface of the sapphire substrate 10 is exposed on the side surface 100aa of the first groove 100a, and the a surface is exposed on the bottom surface 100ab. The width L1 of the first groove 100a is preferably 0.1 to 20 μm, and the distance L2 between the first grooves 100a is preferably 0.1 to 20 μm. This is because the light extraction efficiency can be further improved. More preferably, the width L1 is 0.1 to 5 μm and the interval L2 is 0.1 to 5 μm. An angle θ1 of the side surface 100aa of the first groove 100a with respect to the main surface of the sapphire substrate 10 is preferably 40 to 80 °. Similarly, the light extraction efficiency can be further improved. More desirably, the angle is 50 to 70 °. The depth D1 of the groove 100a is desirably 0.1 to 5 μm. Similarly, the light extraction efficiency can be further improved. More desirably, the thickness is 0.1 to 5 μm.

  The second stripe shape 101 has a plurality of second grooves 101a arranged at equal intervals in parallel to a direction orthogonal to the x-axis direction (y-axis direction in FIG. 2, corresponding to the second direction of the present invention). Yes. The y-axis direction is the m-axis direction of the sapphire substrate 10. The bottom surface 101ab of the second groove 101a is flat, and there is no unevenness along the first stripe shape 100. The cross section of the second groove 101a in the zx plane is rectangular, the c-plane of the sapphire substrate 10 is exposed on the side surface 101aa of the second groove 101a, and the a-plane is exposed on the bottom surface 101ab. The width L3 of the second groove 101a is preferably 0.1 to 20 μm, and the distance L4 between the second grooves 101a is preferably 0.1 to 20 μm. This is because the light extraction efficiency can be further improved. More preferably, the width L3 is 0.1 to 5 μm and the interval L4 is 0.1 to 5 μm. The depth D2 of the second groove 101a (the depth from the top surface of the sapphire substrate 10 to the bottom surface 101ab of the second groove 101a) is arbitrary as long as the bottom surface 101ab of the second groove 101a is flat. However, in order to improve the light extraction efficiency due to the difference between the depth D2 of the second groove 101a and the depth D1 of the first groove 100a, D2 may be 0.1 to 2 times D1. desirable.

A region on the surface of the sapphire substrate 10 other than the groove 101a side surface 101aa and the bottom surface 101ab of the second stripe shape 101 is covered with an insulating film 17 made of SiO ₂ . The thickness of the insulating film 17 is 5 to 100 mm. In addition to SiO ₂ , Si ₃ N ₄ , ZnO, TiO ₂ , ZrO ₂ , etc. can be used for the insulating film 17.

  In the group III nitride semiconductor light emitting device of Example 1, the first stripe shape 100 provided on the sapphire substrate 10 is arranged in the x-axis direction, which is the stripe direction of the first stripe shape, as shown in FIG. It is divided by the second stripe shape 101 having the orthogonal y-axis direction as the stripe direction, and light propagating in the x-axis direction can be reflected and extracted. Therefore, the light extraction efficiency is improved as compared with the conventional group III nitride semiconductor light emitting device provided with only the first stripe shape 100. Further, the group III nitride semiconductor light-emitting device of Example 1 has an internal quantum efficiency improved because the m-plane is the main surface.

  Next, a method for manufacturing the group III nitride semiconductor light-emitting device of Example 1 will be described with reference to FIGS.

  First, the uneven | corrugated process to the sapphire substrate 10 is demonstrated. First, as shown in FIG. 3A, first grooves 100a parallel to the x-axis direction are periodically formed at predetermined intervals on the surface of the sapphire substrate 10 having the a-plane as a main surface by photolithography and dry etching. The arranged first stripe shape 100 is formed. The m-plane of sapphire is exposed on the side surface 100aa of the first groove 100a, and the a-plane of sapphire is exposed on the bottom surface 100ab.

Next, as shown in FIG. 3B, an insulating film 17 made of SiO ₂ is formed on the entire surface of the sapphire substrate 10 along the irregularities of the first stripe shape 100 by vapor deposition. The insulating film 17 may be formed by sputtering, CVD, or the like in addition to vapor deposition.

  Next, as shown in FIG. 3C, the first stripe shape 100 on the surface of the sapphire substrate 10 is formed on the surface of the sapphire substrate 10 by photolithography along the unevenness of the first stripe shape, and y orthogonal to the x-axis direction. Striped photomasks 103 are formed periodically arranged at predetermined intervals parallel to the axial direction.

  Next, as shown in FIG. 3D, the insulating film 17 not covered with the photomask 103 is dry-etched, and then the surface of the sapphire substrate 10 exposed by removing the insulating film 17 is dry-etched. Here, the convex portion of the sapphire substrate 10 has a convex corner as the dry etching progresses, and the height of the convex portion gradually decreases. For this reason, the etching bottom surface can be made flat if sufficient etching time is taken. Further, the etching can be performed deeper than the depth D1 of the first groove 100a. As a result, a second stripe shape 101 is formed in which second grooves 101a that are parallel to the y-axis direction and have a flat bottom surface are periodically arranged at predetermined intervals. The c-plane of the sapphire substrate 10 is exposed at the side surface 101aa of the second groove 101a, and the a-plane of the sapphire substrate 10 is exposed at the bottom surface 101ab of the second groove 101a.

  Next, the photomask 103 is removed. As described above, the sapphire substrate 10 having the uneven shape shown in FIG. 2 can be formed.

  Next, the process of manufacturing the group III nitride semiconductor light-emitting device of Example 1 having the m-plane as the main surface using the sapphire substrate 10 with the uneven shape obtained as described above will be described.

  First, a buffer layer (not shown) made of AlN is formed by magnetron sputtering without performing thermal cleaning that is usually performed to recover damage to the sapphire substrate 10 due to etching. The buffer layer may be formed by forming a thin Al film and then nitriding by supplying a nitrogen source such as ammonia. In addition, the buffer layer may be formed by sputtering other than magnetron sputtering, MOCVD, or the like. In addition to AlN, GaN, AlGaN, AlInN, AlGaInN, or the like may be used for the buffer layer. However, from the viewpoint of lattice matching with sapphire, the Al composition ratio of the buffer layer material is desirably high, and AlN is most desirable.

  Next, the sapphire substrate 10 on which the buffer layer is formed is carried into an MOCVD apparatus, and the temperature is raised to the crystal growth temperature in the next step in an atmosphere containing hydrogen and ammonia.

Then, the GaN crystal 104 is grown from the side surface 101aa of the second groove 101a through the buffer layer by MOCVD. The GaN crystal 104 grows so that the c-axis direction of the sapphire substrate 10 matches the c-axis direction of the GaN crystal. Here, the source gas used in the MOCVD method is ammonia (NH ₃ ) as a nitrogen source, trimethyl gallium (Ga (CH ₃ ) ₃ ) as a Ga source, and H ₂ or N ₂ as a carrier gas.

  Since the surface of the sapphire substrate 10 other than the side surface 101aa and the bottom surface 101ab of the second groove 101a is covered with the insulating film 17, no GaN crystal grows from those surfaces. Therefore, the GaN crystal 104 is made of AlN so that the GaN crystal 104 does not grow from the bottom surface 101ab, and the growth in the c-axis direction is dominant as the growth direction of the GaN crystal grown from the side surface 101aa of the second groove 101a. The thickness of the buffer layer and the growth temperature of the GaN crystal 104 are adjusted. For example, the thickness of the AlN buffer layer is the AlN provided between the sapphire substrate and GaN when the GaN is epitaxially grown flat in the c-axis direction with the direction perpendicular to the main surface of the sapphire substrate being the c-axis direction of GaN. The growth temperature of the GaN crystal 104 may be lower than the growth temperature when epitaxially growing GaN with the direction perpendicular to the main surface of the sapphire substrate as the c-axis direction. . The buffer layer of AlN having such a minimum thickness is usually formed with a sputtering time of 40 seconds, which is 150 to 200 mm in thickness. Further, the growth temperature when epitaxially growing GaN usually with the direction perpendicular to the main surface of the sapphire substrate as the c-axis direction is higher than 1100 ° C. Therefore, by setting the thickness of the AlN buffer layer to 150 mm or less and the growth temperature of GaN to 1100 ° C. or less, the GaN crystal 104 is prevented from growing from the bottom surface 101ab, and from the side surface 101aa of the second groove 101a. The growth in the c-axis direction can be dominant as the growth direction of the growing GaN crystal.

  When the GaN crystal 104 is grown in this manner, the GaN crystal 104 grows faster in the c-axis direction (−c direction), that is, in the second groove 101a in the direction parallel to the sapphire substrate 10, It grows little by little in the direction perpendicular to the sapphire substrate 10 (FIG. 4A). As the growth proceeds further, the second groove 101a is filled with the GaN crystal 104, and the surface of the sapphire substrate 10 is gradually covered with GaN by the growth in the direction parallel to the sapphire substrate 10 (both in the −c direction and the + c direction). Finally, a flat GaN crystal (base layer 18) is formed on the sapphire substrate 10 (FIG. 4B). The principal surface of the GaN crystal of the base layer 18 is an m-plane. This is because the main surface of the sapphire substrate 10 is the a-plane and the side surface 101aa of the second groove 101a is the c-plane, which is caused by a difference in lattice constant between GaN and sapphire.

  The base layer 18 formed as described above is composed of a GaN crystal grown only from the side surface 101aa of the second groove 101a that is the c-plane of sapphire. Therefore, the base layer 18 has a small variation in the plane orientation of the GaN crystal, and can improve the crystallinity of the GaN.

Next, the n-type layer 11, the light emitting layer 12, and the p-type layer 13 are sequentially laminated on the base layer 18 by MOCVD (FIG. 4C). The source gas used in the MOCVD method is the same as that for forming the base layer 18 for the nitrogen source and the Ga source. Trimethylindium (In (CH ₃ ) ₃ ) is used as the In source, and trimethylaluminum (Al (CH ₃ ) is used as the Al source. ₃ ), the n-type doping gas is silane (SiH ₄ ), the p-type doping gas is cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ), and the carrier gas is H ₂ or N ₂ .

Next, a part of the p-type layer 13 and the light-emitting layer 12 was removed by dry etching to expose the surface of the n-type layer 11, and a transparent electrode 15 was formed and exposed on almost the entire surface of the p-type layer 13. An n-electrode 14 is formed on the surface of the n- type layer 11, and a p-electrode 16 is formed on the transparent electrode 15. Thus, the group III nitride semiconductor light emitting device of Example 1 shown in FIG. 1 is manufactured.

  As described above, when a group III nitride semiconductor light-emitting device having an m-plane as a main surface is grown by growing GaN from the concavo-convex side surface using the sapphire substrate 10 having the concavo-convex shape, FIG. The sapphire substrate 10 formed as described above is used. In the sapphire substrate 10, the first stripe shape 100 is divided by the second stripe shape 101, and a step is generated in an arbitrary x-axis direction. Therefore, light propagating in the x-axis direction can be reflected and light can be extracted outside. Moreover, only the side surface 101aa and the bottom surface 101ab of the second groove 101a are exposed on the surface of the sapphire substrate 10 by being covered with the insulating film 17. Since the side surfaces 101aa are all c-planes of sapphire, when the base layer 18 is formed by crystal growth of GaN from the side surfaces 101aa, the crystal plane orientation is aligned, so that the crystal quality of the base layer 18 can be improved.

  In addition, although the manufacturing method of the group III nitride semiconductor light-emitting device of Example 1 was comprised with the group III nitride semiconductor which has m surface as a main surface, this invention is not limited to it, Arbitrary The present invention can be applied to the production of a group III nitride semiconductor light emitting device having a main surface as a surface. In particular, the present invention is suitable for the manufacture of a group III nitride semiconductor light-emitting device whose main surface is a surface having an internal electric field of 10% or less with respect to the internal electric field in the case of c-plane, such as a-plane or (11-22) plane. Is preferred.

Further, the first stripe direction of the stripe-shaped 100 (first direction), the stripe direction of the second stripe shape 101 (the second direction) has been to be orthogonal in Example 1, to give desired Group III nitride It can be arbitrarily set according to the surface orientation of the main surface of the physical semiconductor, that is, according to the surface orientation of the main surface of the sapphire substrate and the surface orientation of the side surface 101aa of the second groove 101a. However, it is desirable to set to 30 to 150 ° for improving light extraction efficiency.

  The group III nitride semiconductor light-emitting device of Example 1 is a face-up type, but the present invention is not limited to this and can also be applied to a flip-chip type.

  The group III nitride semiconductor light-emitting device of the present invention can be used for lighting devices and the like.

10: Sapphire substrate 11: n-type layer 12: light-emitting layer 13: p-type layer 14: n-electrode 15: transparent electrode 16: p-electrode 17: insulating film 18: base layer 100: first stripe shape 101: second Stripe shape 100a: first groove 101a: second groove

Claims (5)

A group III nitride having a nonpolar plane or a semipolar plane as a main surface on the sapphire substrate by forming a stripe shape on the surface of the sapphire substrate and growing a group III nitride semiconductor from the uneven side surface of the stripe shape. In a method for manufacturing a group III nitride semiconductor light emitting device that forms a laminated structure made of semiconductors,
A first step of forming, on the surface of the sapphire substrate, the stripe shape constituted by a plurality of first grooves arranged in stripes parallel to a first direction that is parallel to the main surface of the sapphire substrate. When,
A second step of forming an insulating film on the entire surface along the first stripe shape on the surface of the sapphire substrate;
A third step of forming a resist mask on the insulating film in a stripe shape in which a second direction that forms an angle with the first direction is a stripe direction;
The insulating film in a region not covered with the resist mask is dry-etched, and then the sapphire substrate exposed thereby is dry-etched until the bottom surface of the etching becomes flat to form a second stripe shape. A fourth step;
The resist mask is removed, and from the exposed surface perpendicular to the main surface of the sapphire substrate exposed in the fourth step, a group III nitride semiconductor is crystal-grown in a direction perpendicular to the exposed surface by MOCVD, and the main surface is formed. A fifth step of forming a semiconductor layer made of a group III nitride semiconductor having a nonpolar plane or a semipolar plane;
A method for producing a Group III nitride semiconductor light-emitting device, comprising:   The method for manufacturing a group III nitride semiconductor light emitting device according to claim 1, wherein the first direction and the second direction are orthogonal to each other.   The nonpolar plane is an m-plane, a-plane, or (11-24) plane, and the semipolar plane is (11-22) plane, (20-21) plane, (10-11) plane, (10- 12) The method for producing a group III nitride semiconductor light-emitting device according to claim 1 or 2, wherein the surface is a surface.   4. The group III nitriding according to claim 1, wherein the sapphire substrate has an a-plane as a main surface, and the first direction is a c-axis direction of the sapphire substrate. For manufacturing a semiconductor light emitting device. The exposed surface perpendicular to the main surface of the sapphire substrate exposed in the fourth step is a c-plane of sapphire, and from this c-plane, the group III nitride semiconductor is parallel to the main surface of the sapphire substrate, The method for producing a group III nitride semiconductor light-emitting device according to any one of claims 1 to 4, wherein crystal growth is performed in the c-axis direction of the group III nitride semiconductor.

Images